Optimal compaction of easy-to-process concretes

Easy-to-process concretes (LVB) of flowable consistency (consistency classes F5 and F6) are especially suitable for manufacture of construction elements with complex geometry and a high percentage of reinforcement. A prerequisite for successful application is, in addition to low inclination to segregation, a compaction intensity adapted to the processing properties.

Within the scope of a research project conducted jointly y by the Research Institute of the German Cement Works Association (VDZ) and by Munich Technical University, investigations were carried out of the properties of easy-to-process concretes as a function of compaction intensity.

In the course of the investigation, it became clear that both the flowability and the viscosity of the concretes must be considered when choosing the compaction method and/or compaction intensity. The flowability can, for example, be quantified based on the slump. The viscosity and/or ductility can be classified based on the flowability in the slump test. The investigations showed that sensitivity to the compaction intensity increases with increasing flowability and diminishing ductility. High compaction intensity, for example, resulted in concretes of low ductility and high flowability in pronounced sedimentation of the coarse aggregate (Fig. 1)  and in a slight reduction of compressive strength. These concretes should therefore be only lightly compacted, using for example a manual process such as poking or rodding. Concretes of medium toughness can be compacted somewhat more intensively: e.g., by internal vibrator. Here, care should be taken to ensure an adequate vibration time to prevent sedimentation of the coarse aggregate. Use of concrete of high ductility is recommended only in combination with high flowability (F6) or SCC, since otherwise very intensive compaction is required.

Related articles:

Issue 2019-07 SIKA

Filling and compaction aid for concrete products developed

From now on, the newly developed SikaPaver HC-218 filling and compaction aid is available to the concrete product industry. The product on the basis of an innovative formulation minimizes the...

more
Issue 2013-02 Critical observations

Flowable Filling concrete in practice

Specific tasks in concrete construction, e.g. supplementing concrete in thin layers, can only be realized with flowable concrete. For these purposes, special types of flowable concretes have been in...

more
Slipform pavers

Influence of Additives and Admixtures on the Thixotropic Properties of Pastes

To date, low- or no-slump concretes have been used for placement in the slipform paving process to create concrete road pavements. It is thus imperative to compact the concrete using internal...

more
Issue 2020-02 New approaches for testing and evaluation under vibration

Stability of modern concrete

Background The notion of “modern” or contemporary concretes is used as a reference to concretes with relevant PCE-based plasticizer ratios. Nowadays, such types of concrete are used not only for...

more
Issue 2012-06

Wall Forming System

(10) US 8,153,046 B2 (22) Aug. 27, 2008 (45) Apr. 10, 2012 (76) John M. McCary, Binningbam, AL (US) (57) A wall forming system utilizing flowable construction materials, such as concrete, to construct...

more